1. Field of the Invention
The present invention relates to an ink jet recording method for recording by discharging recording liquid. More particularly, the invention relates to a recording method and a recording apparatus using an ink jet head structured by arranging a plurality of elemental substrates.
2. Related Background Art
A liquid jet recording method by discharging recording liquid, such as ink, from discharge ports by the utilization of thermal energy in order to cause it to fly and adhere to a paper sheet, a plastic sheet, a cloth, or other recording media. This is a recording method of non-impact type that generates less noises, and also, makes it easy to record color images, among other advantages, because there is no particular limit to the kinds of recording media to be used.
An apparatus embodying such liquid jet recording method, that is, a liquid jet recording apparatus, is simply structured comparatively. Also, with this apparatus, it is comparatively easy to perform operation at higher speeds because, among other advantages, its liquid jet nozzles can be arranged in higher densities.
Therefore, the liquid jet recording method described above has attracted public attention, with the result that many studies and researches on the method are being carried on. As a matter of fact, several kinds of liquid jet recording apparatuses that embody the liquid jet recording method are currently on the market and practically in use.
Now, in the field where recording is practiced using the liquid jet recording method, it has been desired in recent years to materialize the earlier provision of a recording apparatus capable of recording in higher quality of recorded images at higher speeds. With a view to complying with the request for higher speed recording, studies have been made assiduously on a large-sized recording head, the so-called line head that provides a recording width corresponding to the width of a recording medium to be used so as to make recording possible on a wider recording media.
For such line recording head, however, it is extremely difficult to perfectly process the discharge energy generating elements, driving circuits and the like to drive them, which should be provided to cover almost the entire width of the recording area. Like this, the difficulty lies in enhancing the production yield of this type of recording head.
In other words, for a line recording head that records on an A3 sized recording sheet with a recording density of 400 DPI (dot per inch), it is necessary to process 4,736 discharge energy generating elements (each comprising a pair of electrodes and a heat generating resistor between them for the bubble jet method) without even a single defect: everyone of them should be perfectly processed, hence making its production extremely difficult. As a result, the head costs are so high that it is far beyond practical use.
In order to solve the problem, various methods have been proposed as disclosed in Japanese Patent Laid-Open Application No. 55-132253, Japanese Patent Laid-Open Application No. 2-2009, Japanese Patent Laid-Open Application No. 4-229278, Japanese Patent Laid-Open Application No. 4-232749, Japanese Patent Laid-Open Application No. 5-24192, U.S. Pat. No. 5,016,023, among others. The technical thought of the proposals disclosed in them is to adopt a method wherein a plurality of heads, each provided with a small number of nozzles comparatively easy to be processed such as 32, 48, 64, or 128 nozzles, are arranged in high precision on one base board (or on both faces thereof) in accordance with the required density of nozzles to be provided. However, for an arrangement of the kind, it is required to provide a plurality of heads arranged in high precision for the formation of a constituent capable of directing ink discharges uniformly. As a result, there is a need for the provision of various devices or apparatuses dedicated to making such arrangement. Also, it is necessary to supply ink and driving signals to each of the heads that form such constituent, respectively. Therefore, it is inevitable that the number of parts will increase so that the recording head necessarily becomes larger and the manufacturing costs rise. Thus, even if the performance of such head is made sufficiently high, the cost and size of the liquid jet recording apparatus using a head of the kind still impede creating more demands on the market.
To cope with this situation, there is proposed a method in which a plurality of substrates (hereinafter referred to as heater boards), each provided with a comparatively small number of discharge energy generating elements, such as 64 or 128 (each of which comprises a pair of electrodes and a heat generating resistor between them for the ink jet recording method), are arranged and bonded on one base board in good precision as required.
In accordance with this method, it is possible to obtain, in a high production yield, an elongated head that has hitherto been attempted to be produced by the application of a technique such as photolithographing process in anticipation of covering the entire recording width without even a single defective element.
In this respect, an ink jet head to which this method is applied is such that a ceiling board is integrally formed with a plurality of ink discharge ports arranged for its one end, and also, with a plurality of grooves conductively connected to each of the discharge ports, which are extended from one end to the other end, and that this ceiling board is joined to a plurality of heater boards so as to cover the heater boards with the plurality of grooves formed on the ceiling board.
FIG. 1 is a view which schematically illustrates the timing to drive the ink jet head whose elongation is implemented by the application of the structure described above, as well as its driving positions. Reference marks HB1, HB2, . . . designate each of the heater boards (elemental substrates) arranged. The mark .smallcircle. schematically represents each dot to be printed. The indications directed from the top to the bottom in FIG. 1 represents the elapse of time. It may be possible to consider that the mark .smallcircle. is not necessary confined to only one dot, but it indicates plural dots that are driven at a time. With the head structured as described above, one or several numbers of nozzles are driven as a group from one end of the heater board, and then, printing signals are given continuously to drive them one after another toward the other end. It is thus arranged to terminate the driving of one cycle (one cycle from A to B) at the other end. Such driving is actuated for each of the heater boards at a time.
However, when observing prints obtained by recording performed by the driving method described above, it is found that density unevenness and displacement of impacted points are conspicuous in the vicinity of each seamed portion of heater boards of the recording head. FIG. 2 shows such state as this.
As described earlier, the recording head of the present invention is structured by providing a plurality of heater boards in the arrangement direction of a plurality of discharge energy generating elements. Therefore, printing disturbance tends to occur on each end portion (each seamed portion) of the heater boards. The present inventors have studied and examined repeatedly to ascertain the causes to bring about such printing disturbance, and obtained the following knowledge:
At first, it is conceivable that the structure of the head itself causes such disturbance for the reasons given below. Depending on the degree of precision in which heater boards are cut; the degree of precision in which the heater boards are arranged; the difference of steps or the like often exists in the thickness direction between heater boards, it is not easy to obtain the perfect close contact between the walls of a ceiling board 200 that constitute liquid paths, and the heater boards 100 over each of the seamed portion between the heater boards. FIG. 3 illustrates such state as this. As shown in FIG. 3, if there is a gap s between the wall 201 that constitutes a liquid path, and the heater board 100, the pressure exerted for the execution of printing escapes therefrom, hence reducing the amount of discharge from the respective orifice. As a result, the density unevenness is brought about, and at the same time, the discharging speed thereof is caused to slow down, hence displacing the point of impact.
Also, due to fine differences between the characteristics of each heater board, there occurs difference as to the average printing density per heater board. Thus, at each seamed portion between heater boards, the difference of density becomes conspicuous.
Secondly, it is conceivable that the driving method applied to recording brings about the disturbance. If the method of driving described above is adopted, that is, while arranging eight or sixteen nozzles as a block, the nozzles are driving per heater board one after another from one end to the other continuously, there tends to occur the reduction of discharge amount and discharging speed with respect to the nozzles at the start of driving and the termination thereof. This is due to the fact that when pressure is exerted by foaming of ink on the respective heat generating unit, such pressure is caused to reach the common liquid chamber arranged behind nozzles, but for the nozzles at end portions, it is easier for such pressure to escape backward because there is no foaming taking place in its adjacent nozzles. Conceivably, therefore, the pressure that should be directed toward the respective orifices becomes less intensified to the extent that the pressure escapes backward.
Also, in accordance the driving method described above, it takes a time t after the nozzle at the one end of each heater board (last nozzle B) has been driven until the nozzle on the other end thereof (first nozzle A) is driven. (This time may be referred to as a time between cycles). During this period of time, the relative position of the recording head and recording sheet is caused to shift. Therefore, on the recording sheet, dots are recorded in the stepped form per driving cycle for each seamed portion between heater boards, thus making such portions more conspicuous.
Because of various factors described above, which are superposed on each seamed portion between the heater boards, it becomes difficult to provide prints uniformly over the entire width of the recording head thus arranged. The resultant quality of recorded images is found yet to be improved.